Fluid control valves are used in a wide variety of applications to control the flow of a fluid. The fluid being controlled may comprise a gas, a liquid, or a combination thereof. In some situations, the fluid may also include suspended particulates. While fluid control valves vary widely in the specific configuration used to open and close a fluid communication path through the valve, one specific type of valve actuation is performed using a solenoid. In solenoid-actuated valves, the solenoid comprises an electric current that passes through an electromagnetic coil, with the coil typically formed around a magnetic core. The coil generally comprises a wire that is wrapped around a plastic bobbin numerous times resulting in a plurality of so-called turns. The energized solenoid generates a magnetic field. The strength of the magnetic field is proportional to the number of turns as well as the electrical current provided to the wire. As is well-known in the art, in order to increase the magnetic field provided by a solenoid, the number of turns can be increased and/or the current provided to the wire can be increased. The magnetic field typically operates on a movable armature connected to a valve member. Typically, the valve also includes a spring or other biasing member that generates a biasing force in opposition to the magnetic field. Therefore, in the absence of a magnetic field generated by the solenoid, the valve member is moved into a normally open or a normally closed position.
FIG. 1 shows a prior art solenoid valve 100. The prior art solenoid valve 100 comprises a housing 101 including a first fluid port 102 and a second fluid port 103. Within the housing 101 is a movable armature 104 that is coupled to a valve seal 113 to control the flow of fluid between the inlet port 102 and the outlet port 103. The movable armature 104 can be biased to open or close the valve with a spring 105. A solenoid can be energized in order to overcome the biasing force of the spring 105. The solenoid comprises a wire coil 106 wrapped around a plastic bobbin 107. As is generally known in the art, the force of the solenoid can be increased by increasing the number of turns, i.e., the number of times the wire coil 106 is wrapped around the bobbin 107. The bobbin 107 is placed over a portion of the movable armature 104 as well as a stationary iron core 108. The stationary core 108 along with a magnetic sleeve 112 that surrounds the coil 106 helps direct the magnetic flux produced when the coil 106 is energized to act on the movable armature 104.
The prior art valve 100 forms a substantially fluid-tight seal between the bobbin 107 and other valve components using a plurality of seals. A first seal 109 forms a substantially fluid-tight seal between the bobbin 107 and the fixed core 108. A second seal 110 forms a seal between the bobbin 107 and a pole piece 111. The seals 109, 110 attempt to prevent fluid from leaking through the valve and reaching the electrical components of the valve. However, the seals 109, 110 are often rubber O-ring seals that can easily degrade resulting in leaking through the valve. If fluid leaks past the seals 109, 110, there is a chance of fluid reaching the coil 106 resulting in an electrical short and rendering the valve 100 useless.
In addition to the potential for leaks associated with the prior art valve 100, the prior art valve 100 can also suffer from power constraints. Although the prior art valve 100 may be able to provide adequate performance if the valve's size is not limited or the pressure flowing through the valve is minimized, if the valve's cross-sectional width, W, or footprint, is limited, then the number of turns available for the coil is also limited. As is generally known, a higher pressure flowing through the valve requires a stronger spring 105, thereby also requiring a higher force applied to the armature 104 in order to overcome the biasing force of the spring 105. With a restricted number of turns, the current supplied to the coil needs to be increased in order to increase the force applied to the movable armature 104. However, increasing the current also increases the heat generated, which may not be desired. Further, increasing the current also increases the costs associated with operating the valve. Although the cross-sectional area of the armature 104 and fixed core 108 could be decreased in order to increase the number of turns, this also has a draw back. The force provided by the solenoid can be understood by equation (1).
                              F          solenoid                =                                            c              1                        ×                                          (                                  N                  ×                  I                                )                            2                        ⁢            A                                s            2                                              (        1        )            
Where:
Fsolenoid is the force provided by the solenoid to the movable armature;
c1 is a constant;
N is the number of turns;
I is the current through the coil;
A is the cross-sectional area of the armature/core interface; and
s is the stroke of the armature.
Therefore, as can be illustrated by equation (1), decreasing the cross-sectional area, A, of the fixed core 108 and armature 104 can also decrease the performance of the valve. Furthermore, the use of the plastic bobbin 107, which is standard on most solenoid valves, limits the space available for the coil. Most plastic bobbins are injection molded and comprise a minimum thickness d1, of around 0.2 mm.
The embodiments described below provide a solenoid valve that is improved by replacing the plastic bobbin 107 of the prior art valve 100 with a thinner metallic tube bobbin. The metallic tube bobbin can be made much thinner and thus, can receive a higher number of turns for a given valve cross-sectional width, W. Further, with the coil being closer to the movable armature, the force applied to the movable armature is further increased.